The present invention relates generally to status indicating circuits and more particularly to status indicating and current limiting circuits for electrical switches in which lamps provide the status indication.
Single filament indicator lamps are commonly utilized in electrical circuits to indicate the status of electrical devices such as switches. For example, a single filament lamp oftentimes is provided in electrical equipment to indicate whether a power switch is open or closed. When the switch is closed, the indicator lamp emits visible light to indicate the status of the switch. When, however, the lamp is not lighted, it is not readily known whether the lamp is defective or whether the switch is open. Consequently, the use of press-to-test circuits has become common to predetermine the status-indicating feature of the indicator lamp. To determine the status of such lamps they may be tested individually or in groups. However, this testing merely indicates the condition of the lamps at the time of the test and does not provide a continuous monitoring of the condition of the filaments of the indicator lamps.
Ballast lamps may be utilized in electrical circuits to limit current flow. Such ballast lamps may be connected in series with other electrical devices to control current surges in a supply line in order to protect the other devices from being damaged by the current surge. However, if the lamp filament should become disabled, electrical current to the other electrical devices is generally interrupted. Furthermore, the use of ballast lamps does not provide a continuous monitoring of the condition of the lamp filament and frequent testing in a manner similar to the testing of indicator lamps is thus required.
It is accordingly an object of the present invention to provide a novel method and current limiting circuit in which the status of the current limiting device is continuously monitored.
It is another object of the present invention to provide a novel method and current limiting circuit in which two current limiting devices are connected in parallel to enhance the reliability for the circuit.
It is yet another object of the present invention to provide a novel method and status indication circuit in which the condition of the indicator lamp is continuously monitored.
Yet still another object of the present invention is to provide a novel method and circuit for both status indication and current limiting functions in which the longevity of the status indication lamps and the longevity of the contacts of the switch whose condition is being monitored are significantly increased.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from the claims and from the perusal of the following detailed description in connection with the appended drawings.